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bug#50268: 28.0.50; Assertion warning during native compilation
From: |
Andrea Corallo |
Subject: |
bug#50268: 28.0.50; Assertion warning during native compilation |
Date: |
Mon, 20 Sep 2021 22:12:32 +0000 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
Michael Welsh Duggan <mwd@md5i.com> writes:
> I was able to determine that there was a bug in the pacproxy.el code
> that I included in the bug report. Fixing that bug caused native
> compilation to work. The assertion and backtrace were not particularly
> useful in determining the bug in the code, though. The bug was in the
> `pacproxy--retrieve-wpad' function when I let-bound the following
> illegal lambda:
>
> (lambda (&rest) "DIRECT")
>
> The fix was to change this to:
>
> (lambda (&rest _) "DIRECT")
>
> Is there another part of the compiler that could have caught this and
> returned a useful diagnostic?
Hi Michael & all,
I had a quick look and these are my findings:
(byte-compile '(lambda (&rest _) "DIRECT"))
=>
#[128 "\300\207" ["DIRECT"] 2 "DIRECT
(fn &rest _)"]
Here we have as encoded signature 128 (one rest arg) and the frame size
is 2 (one for the rest arg and one for the immediate). Fine...
(byte-compile '(lambda () "DIRECT"))
=>
#[0 "\300\207" ["DIRECT"] 1 "DIRECT"]
Here we have as encoded signature 0 (no args) and the frame size is 1
(will be used by the immediate). Fine as well.
(byte-compile '(lambda (&rest) "DIRECT"))
=>
#[128 "\300\207" ["DIRECT"] 1 "DIRECT
(fn &rest)"]
This is the problematic case that was signaled as reproducer. Here we
have as encoded signature 128 (one rest arg) but the frame size (1) is
not accounting for this.
I think this output is a incoherent and I guess the byte compiler should
probably just raise an error and refuse to compile if the lambda list is
invalid. Am I wrong?
Regards
Andrea